Urethral strictures can be congenital or acquired. Acquired urethral stricture is common in men but rare in women. Most acquired strictures are due to infection or trauma. Apart from infections caused by venereal diseases, infection from long term use of urethral catheters and the use of large caliber instruments inserted for medical uses into the urethra causes trauma to the urethra. External trauma, e.g., pelvic bone fractures or saddle injuries, can also cause urethral strictures. These narrowings restrict the urine flow. In chronic cases the bladder muscle becomes hypertrophic, and later an increase in the residual urine may develop in the bladder. Prolonged obstruction may cause incompetence of the outflow control mechanism resulting in incontinence or high pressures in the bladder resulting in kidney damage and renal failure. Residual urine may be a predisposing factor for urinary infections which include prostatic infections, urethral abscess and also bladder stones.
Urethral strictures can be managed with palliative treatments such as dilatations of the urethra, which are not curative, because dilatation fractures the scar tissue and temporarily enlarges the lumen. As healing occurs, the scar tissue reforms.
Visually controlled internal urethrotomy is also used in the treatment of urethral strictures. However, in most cases the stricture reoccurs and the procedure has to be repeated.
Plastic surgical repair of the stricture is a meticulous and complicated procedure. However, this procedure has a high recurrence of urethral strictures, and because of the lack of enough experienced surgeons for reconstructive surgery, the majority of cases are managed by non-curative methods.
An intraurethral device designed for urethral strictures made of an expandable tubular mesh is described by E. J. G. Milroy et al., in an article which appeared in the Journal of Urology (Vol. 141, May 1989). The device is inserted in a stenotic duct and keeps the lumen open as its inner diameter is larger than the duct lumen. As this device comprises tubular mesh, it becomes incorporated into the urethral wall within 3 to 6 months of insertion, becoming a permanent device and necessitating surgical intervention for its removal.
Bladder outlet obstruction is one of the most commonly encountered disorders in urology. The most frequently occurring anatomical cause of bladder outlet obstruction in males is enlargement of the prostate gland, either by benign hypertrophy or cancer. The prostate is a chestnut-sized gland lying inferior to the bladder and surrounding approximately the first inch of the urethra. As males age, the prostate commonly enlarges--without necessarily being malignant--and tends to gradually narrow or constrict its central opening and thus exert radial, inwardly directed pressure on the prostatic urethra. This condition, known as benign prostatic hyperplasia (BPH), can cause a variety of obstructive symptoms, including urinary hesitancy, straining to void, and decreased size and force of the urinary stream. As the condition gradually worsens, there may be total closure of the urethra and concomitant complete urinary retention. Chronic urinary retention may deteriorate renal function as high intravesical pressure is transmitted to the renal parenchyma.
When intervention is indicated, there has heretofore been no widely accepted alternative to surgery. The preferred surgical procedure is the transurethral resection, wherein a resectoscope is inserted through the external opening of the urethra, and an electrosurgical loop is employed to cut away sections of the prostate gland from within the prostatic urethra. Another surgical intervention is open surgical removal of the gland performed through an abdominal incision. However, as BPH is a typical disease of elderly people, many patients are poor candidates for such major surgery.
Another treatment is balloon dilatation of the prostate. According to that technique, expansion of the prostatic urethra up to a diameter of 3 to 4 cm results in tearing of the prostate commissurae while keeping the prostatic urethra open. The long time efficacy of this treatment has not yet been established. A further treatment is heating the prostatic tissue to a temperature 3.degree. to 5.degree. C. higher than that of the human body, resulting in some histological changes causing some kind of prostatic shrinkage. The efficacy of this treatment is not universally accepted.
Despite the available alternatives to surgery, such as those mentioned above, most high operative risk patients rely on a perpetually worn catheter, as this alternative has proven efficacy for urinary drainage--so far.
A number of devices have been suggested which are said to provide relief from the effects of prostate hypertrophy. European Patent Application No. 027486, which is based upon U.S. patent application Ser. No. 939,754, filed Dec. 9, 1986, describes a balloon expandable stent which is transurethrally inserted and is placed in a stenotic prostatic urethra. The insertion is performed with the aid of a special balloon catheter which is removed after insertion, leaving in the urethra a nonflexible, expanded stent which ensures the maintenance of the open lumen of the prostatic lumen. The lack of flexibility of this stent is a disadvantage due to the high risk of migration of the stent into the bladder. Also, this stent has a mesh design that favors incorporation into the mucosa, thereby becoming a permanent stent, removable only by a major operation.
A full description of the pathology of the male urethra is provided in Campbell's Urology, 5th Edition, 1986, Vol. 1, pages 520-523 and 1217-1234, and Vol. 3, pages 2860-2886 (published by W. B. Saunders Co., Philadelphia, Pa. U.S.A.), which description is incorporated herein by reference.